In one method of printing, a design, or a portion of a design, is transferred from a printing plate to a printable substrate inking a surface of the printing plate, tranferring the pattern of ink to an intermediate, print-retaining body, or print pad, by pressing the surface of the print pad against the inked surface so that ink transfers to the pad, and then pressing the inked surface of the pad against the substrate to be printed.
A successful process requires substantially complete transfer to the ink from the printing plate to the print pad, and then from the print pad to the printable substrate. A complete transfer of ink in each step requires a proper balance of adhesion froces between (1) the printing plate and the ink, (2) the ink and print pad, and (3) the ink and the printable substrate. If the ink is formulated to transfer well to the pad, its complete transfer from the pad is made more difficult. Chemical solutions to the problem of balancing the relative adhesive forces between ink and the printing plate, the print pad and the printable substrate require a careful selection of materials, and may result in sacrificing some print quality in the finished printed product.
Another difficulty with chemical solutions to the problems of ink transfer is that different substrates may require different ink formulations. For example, U.S. Pat. No. 4,388,137 to McCarty et al, describes coatings which are specifically designed to provide a desired degree of differential adhesion to cling to different surfaces by controlling (1) the density of cross-linking in the coatings, (2) the presence of adhesion-promoting sites in the coating, and (3) the glass transition temperature of the coating.
A method of printing by transferring ink from one surface to another which does not require a delicate balance between the adhesive properties of an ink with respect to the surfaces from which and to which it is to be transferred, is desirable.